Object recognition is a central topic of research in visual perception and cognitive neuroscience. However, little is known about the nature of object representations in the human brain. What features do we use to recognize objects? How does the brain represent these features? Novel high-resolution fMRI techniques being developed in our lab allow us to examine object representations at a much finer scale than standard fMRI, with voxels as small as 0.5x0.5xlmm. High resolution fMRI provides activations that are more localized and have higher contrast to noise than standard fMRI. Using high resolution fMRI, we propose to develop a new approach to find the set of object images or features that optimally activate regions within object-selective cortex. We propose to examine the fine-scale functional organization of object representation in humans using an event-related design in which we will examine the responses to individual images of objects without pregrouping images into sets that share common features or belong to the same category. In Aim 1 we will examine the reliability of responses to individual object images across trials, and find whether the group of optimal stimuli for activating a given region corresponds to grouping by features, objects or categories. In Aim 2 we will test the hypothesis that certain features, locations and spatial frequency bands within an image account disproportionately for object classification. If we find diagnostic features for object classification, we will then examine using high resolution fMRI whether responses in object-selective cortex correspond to the presence of diagnostic features and whether these activations predicts success at object categorization. Our proposed research will provide: (i) new methods for high resolution fMRI in clinical scanners, (ii) novel approaches for examining object representations in humans and (iii) a comprehensive multidisciplinary study to understand the neural basis of object recognition. Results of these experiments will provide critical constraints on any theory of object recognition.